Lazy

This module provides a type Lazy.t and functions to create and manipulate lazy values. A lazy value is a value that is not computed until it is needed. This is useful for deferring computations that may be expensive or unnecessary.

The type of a lazy value. Lazy.t<'a> represents a lazy value that will eventually yield a value of type 'a when accessed. The value is computed only once, and the result is cached for subsequent accesses. If the computation throws an exception, the same exception is thrown again on subsequent accesses.

Lazy.make(f) creates a lazy value from f which is the computation to be deferred of type unit => 'a. The function returns a lazy value of type Lazy.t<'a>.
The computation is not executed until the lazy value is accessed.

## Examples 
```rescript 
let lazyValue = Lazy.make(() => {
  // Some expensive computation
  Console.log("Computing...")
  42
});
lazyValue->Lazy.get->assertEqual(42)
```

Lazy.get(x) forces the suspension x and returns its result. If x has already been forced, Lazy.get(x) returns the same value again without recomputing it. If it threw an exception, the same exception is thrown again. Throw Undefined if the forcing of x tries to force x itself recursively. This is a runtime error.

Lazy.isEvaluated(x) returns true if the suspension x has already been forced and did not throw an exception. Otherwise, it returns false. This is useful for checking if a lazy value has been computed before accessing it.

## Examples
```rescript 
let lazyValue = Lazy.make(() => {
  // Some expensive computation
  Console.log("Computing...")
  42
})
Lazy.isEvaluated(lazyValue)->assertEqual(false)
lazyValue->Lazy.get->assertEqual(42)
lazyValue->Lazy.isEvaluated->assertEqual(true)
```

force(x) forces the suspension x and returns its result. If x has already been forced, Lazy.force(x) returns the same value again without recomputing it. If it threw an exception, the same exception is thrown again. Throw Undefined if the forcing of x tries to force x itself recursively.

force_val(x) forces the suspension x and returns its result. If x has already been forced, force_val(x) returns the same value again without recomputing it. Throw Undefined if the forcing of x tries to force x itself recursively. If the computation of x throws an exception, it is unspecified whether force_val(x) throws the same exception or Undefined.

Lazy.from_fun(f) creates a lazy value from f which is the computation to be deferred of type unit => 'a. The function returns a lazy value of type Lazy.t<'a>.
The computation is not executed until the lazy value is accessed.

from_val(v) returns an already-forced suspension of v. This is for special purposes only.

is_val(x) returns true if `x has already been forced and did not throw an exception.